The present invention is directed to a wave-guide structure comprising a wave-guide layer applied to a substrate, which wave-guide layer has incorporated therein a thin multi-layer system, for use in optical communication techniques and method for producing the wave-guide structure.
Wave-guide structures which include modulators of an integrated construction, laser amplifiers and coupling devices have been disclosed in an article by Miller, The Bell System Technical Journal, Volume 48, 1969, pp. 2059-2969 and in an article by E. A. Aschmoneit, Elektrotechnische Zietschrift, Volume 22, 1970, pp. 499-501. These references also disclose various processes for producing the above-mentioned wave-guide structures.
The construction and properties of multi-layers were described in a book, H. A. Macleod, Thin Film Optical Filters, Adam Higler, Ltd., London, 1969, pp. 37-87, 154-199, and 301-304. Utilizing the theory described in this book, it is possible to construct multi-layer systems from dielectric thin layers which change the spectral or polarization properties of the optical radiation in a purposeful fashion or serve as reflectors. For example, the properties of the optical radiation can be changed by constructing a multi-layer system as either a narrow-band interference filter, a beam divider, or a system for improving the optical properties.
When constructing a polarizer for light waves directed onto a multi-layer system and likewise when constructing a spectral-selective filter, the number of layers having high and low indexes of refraction, the relationship of the indexes of refraction, and the inclination of the layers to the direction of propagation of the light waves are important. The particular relationship of the number of layers, their index of refraction and their inclination are discussed in the German Printed Application P 22 52 826.3.
To provide a non-polarizing beam splitter for light waves which have a wave length .lambda.0, all the layers of the multi-layer system require an effective optical thickness which is equal to an odd number multiple of .lambda.0/4. In addition, the inclination of the surface of the multi-layer system is selected so that the reflectance is the same for the components of the radiation which falls on this system, which components oscillate at right angles and parallel to the incidence plane. A detailed discussion of these requirements is contained in the German Printed Application P 23 32 254.5.